After losing her husband, Ai lives with her stepson. Her adolescent son finds the young and beautiful Ai stimulating, and Ai, who felt lonely, begins to develop feelings for her son. One day, the two have a physical relationship, and Ai begins to feel guilty towards her husband and father, which makes her feel closed off. To unwind, they decide to go on a trip to a hot spring together. The mistake is repeated... The mother washes her son's penis, and the son becomes aroused by her and gets an erection. A story of forbidden love and incest where the twisted affection between mother and son intersects in a lascivious way at a hot spring resort.